The usual prior art intraocular lens is rigid, and it is formed, for example, of an appropriate transparent plastic such as methylmethacrylate. U.S. Pat. No. 4,573,998 discloses an intraocular lens which comprises a deformable optical zone with prescribed memory characteristics. The optical zone of the lens disclosed in the Patent may be deformed by rolling or folding the lens to a reduced diameter so that it may be inserted into the eye through a relatively small incision. A deformable intraocular Fresnel lens is disclosed in copending application Ser. No. 46,694 filed May 7, 1987 in the names of the present inventors.
Prior to the introduction of foldable intraocular lenses, such as those disclosed in the aforementioned patent and patent application, there was little need for insertion instruments. With the hard intraocular lenses, conventional surgical procedures and available surgical tools were sufficient for inserting the lenses. However, the advent of the soft foldable lens, coupled with the desire for small incision surgery, created a need for special insertion instruments, by which the lenses could be inserted through the relatively small incisions.
Copending application Ser. No. 5,105 filed Jan. 20, 1987 in the name of Stephen G. Hauser discloses and claims an improved instrument for folding or otherwise deforming deformable intraocular lens for convenient insertion of the lens into the eye through a small incision. The present invention, likewise, is concerned with an insertion instrument for such a purpose.
The insertion instrument of the present invention provides a convenient means for changing the cross-sectional area of a deformable intraocular lens so that the lens will pass through a relatively small incision. The instrument is capable of changing the cross-sectional area of the lens sufficiently so that it will pass through a relatively small incision, without moving into the eye with excessive force, or at excessive speed, after the lens has passed into the eye through the incision. Accordingly, the instrument of the invention prevents a permanent change in the shape of the lens after it has passed into the eye through the incision, and it also prevents damage to the lens and to the eye of the patient after it has entered the eye.
A feature of the insertion instrument of the invention is that it allows a trained nurse to place the lens in the instrument up to the point where the instrument is placed in the eye of the patient. This permits the surgeon to concentrate on the removal of the existing lens. The nurse then hands the instrument to the surgeon ready for the implantation of the new lens into the eye of the patient. This has the obvious advantage in that it relieves the surgeon from performing relatively trivial operations.
The insertion instrument of the invention is also constructed to provide the surgeon with an automatic overload protection so as to avoid the creation of potentially dangerous and hazardous conditions in the patient's eye. This is most important because, to avoid damage and injury to the patient, it may be shown that as the size of the incision decreases a corresponding reduction in force must be made for safety reasons as the lens leaves the incision and enters the eye. Accordingly, the feature of the instrument of the present invention which provides an automatic means for limiting the force that may be applied to the lens as it is inserted through the incision is most important.
The intraocular lens insertion instrument to be described herein, as mentioned above, is particularly suitable for inserting a foldable lens through a small size incision into the eye. The ultimate placement of the lens within the eye, whether anterior or posterior, is of less importance since once the lens has passed through the sclera its ultimate placement depends upon the skill of the surgeon.
It will become apparent as the description proceeds, that the instrument of the invention may also be used for the insertion of lenses designed to provide a refractive correction for other than cataract patients, that is, for refractive surgery patients.
The shape of the interior of the insertion tube is critical to reducing the insertion force required. Emperical research has demonstrated that the transition in the insertion tube from one diameter to another diameter, even though well lubricated must be not only smooth but very gradual. Any abrupt changes in this area manifest themselves in increased insertion forces and possible damage to the lens, that is, separated haptic, torn optical area, and the like.
The probe associated with the force limiting insertion probe must be stiff enough to transmit the insertion force without bending excessively. Yet it must be soft enough to preclude damaging a relatively soft lens. The best results have been obtained from a composite construction. Such a construction may consist of a hard steel core encased in a soft plastic sheath.